Oncostatin M reprogrammes cardiac fibroblasts toward an immunoregulatory state

Background & Objective The timely resolution of inflammation is a prerequisite for effective cardiac repair. While cardiac fibroblasts (CFs) are known to modulate post-injury inflammation and subsequent tissue recovery, the underlying molecular mechanisms remain incompletely defined. Oncostatin M (OSM), a pleiotropic cytokine of the interleukin-6 family, has been identified as a potential mediator that promotes myocardial healing and attenuates fibrosis. This study aims to investigate whether OSM facilitates immune-favorable environments by reprogramming cardiac fibroblasts. Methods We performed ligand-receptor interaction mapping using CellChat on published neonatal myocardial infarction (MI) single-cell RNA sequencing (scRNA-seq) datasets to identify immune–fibroblast crosstalk. Cultured neonatal mouse CFs were treated with OSM, followed by bulk RNA-seq and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. To assess functional paracrine effects, RAW264.7 macrophages were cultured in OSM-primed fibroblast-conditioned medium, with inflammatory gene expression quantified by qRT–PCR. Furthermore, Ingenuity Pathway Analysis (IPA) was employed to predict upstream regulators, and C/EBPβ chromatin occupancy was profiled via CUT&Tag. Results CellChat analysis revealed intensive communication between myeloid cells and fibroblasts post-infarction, specifically highlighting the OSM signaling axis. OSM treatment significantly remodeled the CF transcriptome, particularly inducing a robust shift in the secretome enriched for inflammatory regulatory pathways. Functionally, conditioned medium from OSM-treated CFs effectively polarized RAW264.7 macrophages toward a pro-resolving phenotype, characterized by the downregulation of pro-inflammatory markers (e.g., Tnf, Il1a) and the upregulation of anti-inflammatory transcripts (e.g., Il10, Arg1). Notably, OSM also suppressed fibroblast-mediated antigen-presentation programs, including major histocompatibility complex class II (MHC-II) genes. Mechanistically, IPA prioritized C/EBPβ as a key transcriptional driver, a finding supported by CUT&Tag data showing increased C/EBPβ occupancy at genomic loci associated with immunomodulatory genes. Conclusions Our findings demonstrate that OSM induces an immunoregulatory program in cardiac fibroblasts. This reprogramming, characterized by secretome modification and the suppression of MHC-II-mediated antigen presentation, serves to dampen pro-inflammatory macrophage responses and foster a reparative environment following cardiac injury.